Field of the Invention
The present invention relates to an acceleration and deceleration system, and more particularly to an acceleration and deceleration system for an electric motor employed to drive a movable member of a machine tool, a robot hand, or the like.
Description of the Related Art
Movable members of machine tools, robot hands, and the like are generally driven by electric motors such as servomotors. When driving a movable member of a machine tool or moving a robot hand, the electric motor is preferably accelerated or decelerated so as not to apply a shock or vibration to the mechanical system at the time the motor starts to rotate or is stopped. As one acceleration and deceleration system, there is known a system for exponentially increasing or decreasing the rate f of pulses controlling the servometer, as shown in FIG. 5.
In such an exponential acceleration and deceleration system, the acceleration and deceleration control may be carried out entirely irrespective of interpolation of commanded feed speed and displacement, and if interpolation is started, acceleration is caused, whereas if interpolation is finished, deceleration results. The exponential acceleration and deceleration system is advantageous in that the interpolator and acceleration and deceleration circuit are simple in arrangement. Since, however, this system involves an inherent lag upon acceleration and deceleration, the lags of the axes cannot be equalized in circular interpolation under two-axis control, resulting in a disadvantage in that the path which results from exponential acceleration and deceleration is subjected to an error.
To eliminate this error, there has been proposed an acceleration and deceleration system for reducing the path error in circular interpolation by effecting linear acceleration and deceleration as shown in FIG. 3 using a given time constant (see Japanese Patent Application No. 57-172863, for example).
However, as is apparent from FIG. 3, the linear acceleration and deceleration system has the problem that the controlled speed is not smooth and is subject to abrupt changes as compared with the exponential acceleration and deceleration control, and the mechanical system suffers shocks or vibration as the speed goes through the abrupt changes when an axis starts moving or is decelerated.